Index: firmware/App/Modes/ModeTreatment.c
===================================================================
diff -u -rd608769332d4ffe19f39a18caca14d6155f13e0a -r6f5bb3935a079cf48c836b2227db430c069bac40
--- firmware/App/Modes/ModeTreatment.c	(.../ModeTreatment.c)	(revision d608769332d4ffe19f39a18caca14d6155f13e0a)
+++ firmware/App/Modes/ModeTreatment.c	(.../ModeTreatment.c)	(revision 6f5bb3935a079cf48c836b2227db430c069bac40)
@@ -1101,6 +1101,9 @@
     S32 timeDiff = 0;
     F32 rateDiff = 0.0;
     HD_OP_MODE_T currMode = getCurrentOperationMode();
+    S32 txSecRem = CALC_TREAT_TIME_REMAINING_IN_SECS();
+    S32 txMinEla = CALC_ELAPSED_TREAT_TIME_IN_SECS() / SEC_PER_MIN;
+    F32 txMinRem = (F32)txSecRem / (F32)SEC_PER_MIN;
 
     // Reset pending UF/time settings changes to current values in case request is rejected
     pendingUFVolumeChange = presMaxUFVolumeML;
@@ -1115,9 +1118,12 @@
     {
         DIALYSIS_STATE_T currDialysisState = getDialysisState();
         UF_STATE_T currUFState = getUltrafiltrationState();
-        F32 uFRate = uFVolume / ((F32)presTreatmentTimeSecs / (F32)SEC_PER_MIN);                // What UF rate would be if user selected to adjust it
-        U32 trtTime = (S32)( uFVolume / presUFRate ) + 1;                                       // What the treatment duration would be if user selected to adjust it
-        U32 dialVolume = getTreatmentParameterU32( TREATMENT_PARAM_DIALYSATE_FLOW ) * trtTime;  // What dialysate volume would be if user selected to adjust time
+        F32 colUFVol = getUltrafiltrationReferenceVolume();                                          // How much UF volume have we taken so far?
+        F32 remUFVol = uFVolume - colUFVol;                                                          // What would remaining UF volume be after subtracting UF volume already taken
+        F32 remUFVolCap = RANGE( remUFVol, 0.0F, (F32)MAX_UF_VOLUME_ML );                            // Enforce valid range on remaining UF volume
+        F32 uFRate = remUFVolCap / txMinRem;                                                         // What UF rate would be if user selected to adjust it
+        U32 trtTime = ( fabs( presUFRate ) < NEARLY_ZERO ? txMinEla + 1 : (S32)( remUFVolCap / presUFRate ) + txMinEla + 1 ); // What the treatment duration would be if user selected to adjust it
+        U32 dialVolume = getTreatmentParameterU32( TREATMENT_PARAM_DIALYSATE_FLOW ) * trtTime;       // What dialysate volume would be if user selected to adjust time
 
         // UF should already be paused but let's make sure.
         if ( ( TREATMENT_DIALYSIS_STATE == currentTreatmentState ) &&